glcannon - allow 'PREVIEW' as a substitute for 'AXIS' in magic comments

A little more generic for other screens.

Author: c-morley

lib/python/rs274/glcanon.py

@@ -132,7 +132,7 @@ def __init__(self, colors, geometry, is_foam=0):
         self.highlight_line = None
 
     def comment(self, arg):
-        if arg.startswith("AXIS,"):
+        if arg.startswith("AXIS,") or arg.startswith("PREVIEW,"):
             parts = arg.split(",")
             command = parts[1]
             if command == "stop": raise KeyboardInterrupt